This paper deals with a special class of parameter identification problems in structural plasticity. Specifically, we address the problem of identifying yield limits and hardening moduli from knowledge of the displacement response of the structure under a given set of proportional loads. Under the assumptions of piecewise linear holonomic (reversible) plasticity and a suitably discretized structure, the inverse problem can be formulated as a special optimization problem known as a Mathematical Program with Equilibrium Constraints (MPEC), a key feature of which is the presence of complementarity conditions, involving the orthogonality of two sign-constrained vectors. A recently developed numerical scheme, the Penalty Interior Point Algorithm (PIPA), is proposed for solving the identification problem. Some computational results for a hypothetical beam on elastoplastic springs are also given.
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